Shrouded face seal and components thereof

ABSTRACT

One embodiment of the seal housing for a face seal described herein include a base with a seal element support and a shroud both extending from the base in a common direction. The seal element support and the base define a space for receiving a seal element. The shroud includes a tip having a head portion that tapers toward a neck portion that is reduced in size relative to the head portion. The tip is secured to a stem of the shroud through a set of circumferentially distributed countersunk holes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.14/665,068, which was filed on 23 Mar. 2015. U.S. application Ser. No.14/665,068 is a divisional of U.S. application Ser. No. 12/826,629,which was filed on 29 Jun. 2010 and has issued as U.S. Pat. No.9,004,492. U.S. application Ser. No. 12/826,629 is a divisional of U.S.application Ser. No. 11/266,454, which was filed on 11 Nov. 2005 and hasissued as U.S. Pat. No. 7,837,199. Each of these applications isincorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to face seals and particularly to a carbon faceseal whose performance deteriorates in a relatively benign way incomparison to conventional seals.

BACKGROUND

Carbon face seals are used in machinery, such as turbine engines, toeffect a fluid seal between regions of high and low fluid pressure. Forexample, carbon seals are used to prevent hot, high pressure air fromentering a bearing compartment operating at a lower pressure. A typicalcarbon seal for a turbine engine includes an annular carbon ring securedto an annular, nonrotatable, axially translatable seal housing. The sealalso includes a seal seat affixed to a rotatable shaft and positionedaxially adjacent to the carbon ring. The carbon ring comprises a base(or blank) and a nose projecting axially from the base. The nose isurged into contact with the seal seat by a combination of spring forcesacting on the seal housing and the net resultant of axially opposingfluid pressure forces acting on the seal housing and the carbon ring.The contact area between the carbon ring and the seal seat equals theannular area of the nose. The contact between the nose and the seal seatresists fluid leakage across the seal in the radial direction, i.e.toward or away from the axis of rotation of the seal seat.

During operation, the nose gradually wears away. Ordinarily, the seal isreplaced or refurbished before the nose is completely worn away.Occasionally, however, accelerated seal wear can result in complete wearof the nose so that the base of the carbon ring contacts the seal seat.As a result, the contact area between the carbon ring and the seal seatequals the annular area of the base, which is larger than the contactarea of the nose. This affects the resultant of the axially opposingfluid pressure forces such that the net pressure force is less favorablefor maintaining reliable, positive contact between the carbon ring andthe seal seat. Unfortunately, the transition between the normalcondition in which the nose contacts the seal seat, and the highlydeteriorated condition in which the base contacts the seal seat,although it occurs very infrequently, can occur with little warning. Inaddition, more abrupt failure or deterioration of the carbon ring canhave a similar adverse effect on the resultant of the fluid pressureforces. As a result there may be an unanticipated period of engineoperation during which fluid leaks past the seal

What is needed is a carbon seal that deteriorates gracefully in order toexhibit a detectable and benign operating characteristic that clearlyindicates that maintenance is required.

SUMMARY

A face seal assembly according to an exemplary aspect of the presentdisclosure includes, among other things, a seal seat and a seal elementcarried by a seal housing and cooperating with the seal seat toestablish a seal. The seal housing includes a seal element support and ashroud. The shroud includes a tip having a head portion that taperstoward a neck portion that is reduced in size relative to the headportion. The tip is secured to a stem of the shroud through a set ofcircumferentially distributed countersunk holes.

In another exemplary embodiment of the above-described face sealassembly, the shroud is axially elongated relative to the support.

In another exemplary embodiment of any of the above-described face sealassemblies, the seal element includes a blank with a nose extendingaxially therefrom. The blank is stepped so that a first radial regionextends axially beyond a second radial region of the blank.

In another exemplary embodiment of any of the above-described face sealassemblies, the first and second radial regions define respective firstand second steps, and the tip is axially between the first and secondsteps.

In another exemplary embodiment of any of the above-described face sealassemblies, the seal seat is a seal ring, and the seal element is acarbon ring residing radially between the support and the shroud.

In another exemplary embodiment of any of the above-described face sealassemblies, the shroud is radially inboard of the support.

In another exemplary embodiment of any of the above-described face sealassemblies, the seal housing exclusive of the tip is made of a parentmaterial and the tip comprises a second material different than theparent material.

In another exemplary embodiment of any of the above-described face sealassemblies, the second material is selected from the group of materialsconsisting of: a) materials more lubricious than the parent material; b)materials harder than the parent material; and c) materials moreabradable than the parent material.

In another exemplary embodiment of any of the above-described face sealassemblies, the tip is a molded tip.

In another exemplary embodiment of any of the above-described face sealassemblies, the tip completely fills a corresponding one of thecircumferentially distributed holes when the tip is secured to the stemof the shroud.

In another exemplary embodiment of any of the above-described face sealassemblies, the neck portion is positioned radially between the headportion and the seal element.

In another exemplary embodiment of any of the above-described face sealassemblies, the tip is configured to contact the seal seat.

In another exemplary embodiment of any of the above-described face sealassemblies, the seal housing is configured such that all portions of thetip reside radially inside the seal element.

A seal housing for a face seal according to yet another exemplary aspectof the present disclosure includes, among other things, a base with aseal element support and a shroud both extending from the base in acommon direction. The seal element support and the base define a spacefor receiving a seal element. The shroud includes a tip having a headportion that tapers toward a neck portion that is reduced in sizerelative to the head portion. The tip is secured to a stem of the shroudthrough a set of circumferentially distributed countersunk holes.

In another exemplary embodiment of the above-described seal housing, theseal element includes a blank with a nose extending axially therefrom.The blank is stepped so that a first radial region extends axiallybeyond a second radial region of the blank. The first and second radialregions define respective first and second steps, and the tip is axiallybetween the first and second steps.

In another exemplary embodiment of any of the above-described sealhousings, the tip comprises a molded tip.

In another exemplary embodiment of any of the above-described sealhousings, the tip completely fills a corresponding one of thecircumferentially distributed holes when the tip is secured to the stemof the shroud.

In another exemplary embodiment of any of the above-described sealhousings, the neck portion is positioned radially between the headportion and the seal element.

In another exemplary embodiment of any of the above-described sealhousings, the tip is configured to contact the seal seat.

In another exemplary embodiment of any of the above-described sealhousings, the seal housing is configured such that all portions of thetip reside radially inside the seal element.

The foregoing and other features of the various embodiments of thedisclosed seal will become more apparent from the following detaileddescription and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional side elevation view showing an improvedcarbon seal.

FIGS. 2, 3 and 4 are schematic views similar to FIG. 1, butcircumferentially offset from FIG. 1, showing fluid pressure forcesacting on a traditional seal in a normal or normally deterioratedcondition, a highly deteriorated condition and a damaged or severelydegraded condition respectively.

FIGS. 5-8 are schematic views similar to FIGS. 2 through 4 showing fluidpressure forces acting on an improved seal in normal, highlydeteriorated, severely deteriorated and damaged conditions respectively.

FIG. 9 is a view illustrating a seal housing with a shroud whose tip ismade of the same material as the rest of the seal housing.

FIG. 10 is a view similar to FIG. 9 showing a seal housing made of aparent material and having a shroud with a bonded or impregnated tipmade of a second material.

FIGS. 11-13 are views similar to FIG. 9 but with a shroud having a tipin the form of an insert or attachment.

DETAILED DESCRIPTION

Referring to FIG. 1, a shaft 20 for a rotary machine, such as a turbineengine, is rotatable about an axis 22. A seal seat in the form of anannular ring 24 is secured against a shoulder on the shaft by a nut 26.The seal seat extends radially outwardly from the shaft andcircumscribes the axis. The seal seat is one component of a face sealassembly.

The face seal assembly also includes an annular, nonrotatable sealsupport 28 and a pair of annular seal housings 32. Each seal housingincludes a base 34 and a grooved secondary seal holder 36 at one end ofthe base. The secondary seal holder holds a secondary seal 38 in contactwith a cylindrical bore of the seal support. The other end of the sealhousing includes an axially extending shroud 42 and an axially extendingsupport lip 44 that serves as a seal element support. The shroud 42 isradially offset from the lip 44 to define an annular space 46 forreceiving a seal element. The shroud is also axially elongated relativeto the lip. An annular flange 48 with circumferentially distributedslots 50 projects radially outwardly from the lip 44.

The face seal assembly also includes a seal element 52 residing in thespace 46 and secured to the lip 44 by an interference fit. The sealelement includes a base or blank 54 and a nose 56 extending axially fromthe blank. The blank is double stepped such that a first, radiallyinboard region 58 of the blank extends axially beyond a second radiallyoutboard region 60 of the blank to define a first or radially inner step61 and a second or radially outer step 63. Moreover, inner step 61resides axially beyond the tip of shroud 42 whereas outer step 63 doesnot reside axially beyond the shroud tip. In other words, the tip of theshroud is axially between the steps 61, 63. The seal element istypically made of a graphitic carbon material and is often referred toas a carbon element even though it is not made of pure carbon. In theillustrated application, the carbon element is annular and therefore canbe referred to as a carbon ring.

A set of circumferentially distributed support pins such asrepresentative pin 64, each projects axially from the seal support 28and passes through a corresponding slot 50 in the flange 48. Springs 66(depicted in FIGS. 5-8) are circumferentially offset from the pins 64.The springs are compressed between the flange 48 of housing 32 and thesupport 28 so that they exert a force on the flange 48 to urge the noseof the carbon ring into contact with the seal seat 24. The interfacebetween the nose and the seal seat may be unlubricated or “dry” as seenat the left side of the illustration, or it may be lubricated or “wet”as seen at the right side of the illustration. In a wet seal, lubricantflows to the interface by way of circumferentially distributed lubricantpassages 68 in the seal seat.

During engine operation, high pressure air is present in the annularcavity 70 radially inboard of the seal and radially outboard of theshaft 20. Lower pressure air intermixed with oil occupies a bearingcompartment 72, which is the region outboard of the seal. The sealresists leakage of the higher pressure air into the lower pressurebearing compartment.

Referring additionally to FIG. 2, the operation of the above-describedshrouded seal is best understood by first considering a conventionalseal. FIG. 2 shows the conventional seal in a normal or substantiallyundeteriorated condition. FIG. 2 also suffices to show the seal in anormally deteriorated condition, i.e. with the nose only partially wornaway. The arrow F.sub.s represents the force exerted on the seal housing32 by the springs 66. Force graphs f.sub.o and f.sub.c show the axiallyopposing, radially distributed forces F.sub.O, F.sub.C acting on theseal housing, carbon ring and secondary seal as result of the disparatepressures in cavity 70 and compartment 72. The force vectors in graphsf.sub.o and f.sub.c are illustrated as terminating on respective commonplanes to facilitate comparisons of the aggregate pneumatic forces.However those skilled in the art will recognize that the forces actuallyact on the axially facing surfaces of the seal housing, carbon ring andsecondary seal. Graph f.sub.c shows a relatively high pressure acting onthe high pressure side of the seal and a low pressure acting on the lowpressure side of the seal. Graph f.sub.o shows high pressure acting onthe high pressure side of the seal, low pressure acting on the lowpressure side of the seal, and a radially varying pressure in atransition region across the nose 56 of the carbon ring. As is evident,the nose throttles the high pressure down to the low pressure across anarrow radial region. The combination of F.sub.S and F.sub.C exceedsF.sub.O to keep the seal closed.

FIG. 3 shows the conventional seal in a highly deteriorated condition inwhich the nose has been entirely worn away. F.sub.C is the same as inFIG. 2. However because the nose has been worn away, the base portion 54of the carbon ring throttles the high pressure down to the low pressureacross a radial transition region that is relatively wide in comparisonto the transition region of FIG. 2. As a result higher pressure, andtherefore higher forces, act over a larger radial region than is thecase in FIG. 2. Accordingly, the aggregate force F.sub.O acting on thehighly deteriorated seal of FIG. 3 exceeds the aggregate force F.sub.Oacting on the normal or normally deteriorated seal of FIG. 2.Furthermore, F.sub.S is slightly smaller than it is in FIG. 2 due to theincreased spring elongation (decompression) and consequent reduction inspring force. Due to the change in forces acting on the seal, there is apotential for F.sub.O to exceed the combination of F.sub.S and F.sub.Cresulting in separation of the carbon ring 52 from the seal seat 24.This separation will allow leakage through the resulting gap asindicated by the small fluid flow arrows. The force graphs and forceswould be as shown in FIG. 4 if the carbon ring were broken away alongpart or all of its circumference. This would also result in thepotential for leakage as indicated in FIG. 4.

As mentioned previously, the transition between the normal condition inwhich the nose contacts the seal seat, and the highly deterioratedcondition or severely deteriorated conditions occurs very infrequently,but can occur with little warning. As a result there may be anunanticipated period of engine operation during which fluid leaks pastthe seal.

FIG. 5 corresponds to FIG. 2, but shows the improved, double steppedshrouded seal in an undeteriorated or normally deteriorated condition.As is evident, the forces are substantially the same as those of FIG. 2,with the result that the seal is urged closed.

FIG. 6 shows the improved, double stepped shrouded seal in a highlydeteriorated condition similar to the condition of the conventional sealin FIG. 3. The blank of the carbon ring of FIG. 6 includes the firstradial region 58 and its associated step 61 extending axially beyond thesecond radial region 60 and its associated step 63. In addition, theseal of FIG. 5 includes the shroud 42 on the seal housing. The axiallyextended first region 58 throttles the high pressure across a radialtransition region that is radially narrower than the transition regionof FIG. 3. Accordingly, the aggregate force F.sub.O of FIG. 6 is lessthan the aggregate force F.sub.O of FIG. 3. As a result, the carbon ring52 of FIG. 6 is less likely to separate from the seal seat 24 than isthe carbon ring of FIG. 3.

FIG. 7 shows the improved, shrouded seal in a more severely deterioratedcondition. In comparison to FIG. 6, FIG. 7 shows the carbon ring 52 wornback essentially to the shroud 42 and therefore shows a throttlingeffect attributable to the shroud. The shroud and the axially extendedfirst region 58 of the carbon ring throttle the high pressure across aradial transition region that is radially narrower than the transitionregion of FIG. 3. Accordingly, the force magnitude F.sub.O of FIG. 7 isless than the force magnitude F.sub.O of FIG. 3. As a result, the carbonring of FIG. 7 is less likely than the carbon ring of FIG. 3 to separatefrom the seal seat 24 and permit leakage. As further wear of the carbonring occurs, the shroud tip will eventually contact the seal seat 24resulting in a more pronounced throttling effect.

FIG. 8 shows the improved, shrouded seal in a damaged condition in whichthe carbon ring has been broken away over all or part of itscircumference. The shroud 42 contacts the seal element and throttles thehigh pressure across a radially narrow transition so that the sealremains closed and resists leakage.

As is evident, the improved, shrouded seal deteriorates more graduallythan a conventional unshrouded seal. The gradual deterioration isdesirable because it manifests itself as noticeable but minor anomaliesin engine performance. These minor anomalies make the engine operatoraware that seal replacement or repair is required. Such replacement orrepair may then be effected before the seal deteriorates enough to causemore significant problems.

With the construction and operation of the seal having now beendescribed, certain variants may now be better appreciated.

FIG. 9 shows a seal like that of FIGS. 1 and 5-8 in which the housing 32is made of a selected material. The shroud has a tip 74 at its axialextremity remote from the housing base 34. The tip is made of the samematerial as the rest of the housing.

FIG. 10 shows a seal in which the housing 32 is made of a parentmaterial and the shroud has a tip 74 which is a region of the shroudimpregnated with a second material. Alternatively, the shroud tip may bea feature made of or impregnated with a second material and bonded tothe rest of the shroud or may be a coating. The second material may beany material having characteristics that are desirable when the tipcontacts the seal seat 24. These include materials more lubricious thanthe parent material, materials harder than the parent material andmaterials more abradable than the parent material.

FIGS. 11-13 show a seal in which the shroud comprises a stem 76 and atip in the form of an insert or attachment 78 affixed to the stem. InFIG. 11 the insert is affixed with a radially outer snap 82. In FIG. 12the insert is affixed with a radially inner snap 84. In FIG. 13 theinsert is a molded tip secured to the stem 76 through a set ofcircumferentially distributed countersunk holes 86. The tip insert maybe made of a material having characteristics that are desirable when thetip contacts the seal ring 24. These include materials more lubriciousthan the parent material, materials harder than the parent material andmaterials more abradable than the parent material.

Although the improved seal has been shown and described with referenceto specific embodiments thereof, it will be understood by those skilledin the art that various changes in form and detail may be made withoutdeparting from the invention as set forth in the accompanying claims.

We claim:
 1. A face seal assembly, comprising a seal seat and a sealelement carried by a seal housing and cooperating with the seal seat toestablish a seal, the seal housing including a seal element support anda shroud, wherein the shroud includes a tip having a head portion thattapers toward a neck portion that is reduced in size relative to thehead portion, the tip secured to a stem of the shroud through a set ofcircumferentially distributed countersunk holes.
 2. The assembly ofclaim 1, wherein the shroud is axially elongated relative to thesupport.
 3. The assembly of claim 2, wherein the seal element includes ablank with a nose extending axially therefrom, the blank being steppedso that a first radial region extends axially beyond a second radialregion of the blank.
 4. The assembly of claim 3, wherein the first andsecond radial regions define respective first and second steps, and thetip is axially between the first and second steps.
 5. The assembly ofclaim 1, wherein the seal seat is a seal ring, and the seal element is acarbon ring residing radially between the support and the shroud.
 6. Theassembly of claim 1, wherein the shroud is radially inboard of thesupport.
 7. The assembly of claim 1, wherein the seal housing exclusiveof the tip is made of a parent material and the tip comprises a secondmaterial different than the parent material.
 8. The assembly of claim 7,wherein the second material is selected from the group of materialsconsisting of: a) materials more lubricious than the parent material; b)materials harder than the parent material; and c) materials moreabradable than the parent material.
 9. The assembly of claim 1, whereinthe tip is a molded tip.
 10. The assembly of claim 1, wherein the tipcompletely fills a corresponding one of the circumferentiallydistributed holes when the tip is secured to the stem of the shroud. 11.The assembly of claim 1, wherein the neck portion is positioned radiallybetween the head portion and the seal element.
 12. The assembly of claim1, wherein the tip is configured to contact the seal seat.
 13. Theassembly of claim 1, wherein the seal housing is configured such thatall portions of the tip reside radially inside the seal element.
 14. Aseal housing for a face seal comprising a base with a seal elementsupport and a shroud both extending from the base in a common direction,the seal element support and the base defining a space for receiving aseal element, wherein the shroud includes a tip having a head portionthat tapers toward a neck portion that is reduced in size relative tothe head portion, the tip secured to a stem of the shroud through a setof circumferentially distributed countersunk holes.
 15. The seal housingof claim 14, wherein the seal element includes a blank with a noseextending axially therefrom, the blank being stepped so that a firstradial region extends axially beyond a second radial region of theblank, wherein the first and second radial regions define respectivefirst and second steps, and the tip is axially between the first andsecond steps.
 16. The seal housing of claim 14, wherein the tipcomprises a molded tip.
 17. The assembly of claim 1, wherein the tipcompletely fills a corresponding one of the circumferentiallydistributed holes when the tip is secured to the stem of the shroud. 18.The seal housing of claim 14, wherein the neck portion is positionedradially between the head portion and the seal element.
 19. The sealhousing of claim 14, wherein the tip is configured to contact the sealseat.
 20. The seal housing of claim 14, wherein the seal housing isconfigured such that all portions of the tip reside radially inside theseal element.